1. Field of the Invention
This invention relates to a screw-fastened structure for a synthetic resin member, which structure is adapted to fasten and fix the synthetic resin member on a body by means of a screw. The body is in turn mounted on a base via the synthetic resin member.
2. Description of the Prior Art
A tape recorder, especially, a cassette tape recorder is constructed basically as shown in FIG. 8. Namely, a winding reel shaft 2, a rewinding reel shaft 3 and a capstan 4 are provided on a base plate. A pinch roller 5 is provided pivotally relative to the capstan 4. On a head frame 7, a magnetic head 6 is mounted movably in a direction indicated by the arrows.
Further, a motor 8 adapted to drive and rotate the winding and rewinding reel shafts 2,3 and capstan 4 is also mounted on the base plate 1 by way of a motor mount 9 made of a synthetic resin or the like. Incidentally, numeral 10 indicates a tape cassette to be loaded on the tape recorder.
The motor 8 rotates, usually, while producing rotational vibrations. If these vibrations are transmitted to the base plate 1, variations will take place with respect to the state of sliding contact between the magnetic head 6 and a magnetic tape and the feeding speed of the magnetic tape fed by the capstan 4 and pinch roller 5. These variations will lead to reduced recording and playback characteristics of the tape recorder, for example, lowered sound quality.
With the foregoing in view, there has conventionally been adopted such an improvement as shown in FIG. 9 in the fixing of the mount 9 (synthetic resin member) and motor 8 (body to be mounted) so as to avoid transmission of vibrations of the motor 8 to the base plate 1. In an example shown in FIG. 9(a), rubber bushes 11 are attached to the mount 9 and the motor 8 is fixed on the mount 8 by way of the rubber bushes 11. Namely, the rubber bushes 11 are fit in respective insertion holes 12 for motor-fixing screws 13. The screws 13 are caused to extend through central holes of the corresponding bushes 11 and to threadedly engage their corresponding internally-threaded bores (not shown) formed in the upper wall of the motor 8, whereby the mount 9 is held via the bushes 11 between the screw heads of the screws 13 and the upper wall of the motor 8. In this structure, vibrations are absorbed owing to elastic deformations of the rubber bushes ll, so that the transmission of vibrations from the motor to the base plate 1 is suppressed. Turning next to another example illustrated in FIG. 9(b), the mount 9 is formed thinner at areas 9a adjacent to the respective screw insertion holes so that vibrations from the motor 8 are absorbed through elastic deformations of the mount itself.
The above conventional structures are however accompanied by the following problems. In the structure of FIG. 9(a), the elasticity of each rubber bush 11 varies depending on the degree of tightening of its corresponding screw 13. It is hence difficult to draw fully the effects of the rubber bushes 11, which suppress transmission of vibrations by making use of their own elasticity. It is also required to fit the rubber bushes 11 in the mount 9, leading to such inconvenience that their assembly work is cumbersome and moreover, the manufacturing cost is high due to the need for an increased number of components.
On the other hand, the structure depicted in FIG. 9(b) permits easy fixing between the mount 9 and motor 8 by simply tightening the screws without need for any extra parts such as rubber bushes. Even if the screws 13 are tightened firmly, a gap 14 may occur between the screws 13 and mount 9 due to variations in temperature. The formation of the gap 14 results in such problems that the screws 13 are loosened and in some worst cases, fall off due to rotational vibrations of the motor 8.